The present invention relates to a disk type frictional stepless change speed apparatus comprising a drive disk and a driven disk in pressure contact with the drive disk and shiftable along a driven shaft whereby an output of the drive disk is transmitted in varied speeds to the driven shaft, and to an agricultural machine of the type handled by a walking operator and employing the disk type frictional stepless change speed apparatus in its transmission system.
In a the disk type stepless change speed apparatus, the driven disk is pressed very hard against the drive disk to ensure reliable power transmission, and a great force is required to shift the driven disk in this state. A known example of means to reduce this change speed operating force consists in a power actuator such as a hydraulic cylinder as disclosed in the Japanese patent application laid open under No. 56-124927.
Where an actuator is used, however, change speed positions of the driven disk are determined by the actuator operable in response to shift positions of a change speed lever, and it is necessary to provide a feedback mechanism in an actuator control system in order that the relationship between the shift positions of the lever and the change speed positions of the driven disk be an accurate and reproducible one. This renders the apparatus complicated in construction and costly. Furthermore, the use of an actuator permits the driven disk to be slidable with ease while pressed hard against the drive disk, but contributes nothing toward improvement relating to wear of frictional transmission surfaces of the disks occurring in the course of the sliding movements.
The application of the disk type stepless change speed apparatus to a walking operator type agricultural machine has a disadvantage. This type of agricultural machine generally has a transmission system adapted to divide drive from an engine output shaft into two transmission lines, one for propelling the machine and the other for operating an attached working implement. For this purpose the transmission system comprises a first transmission shaft operatively connected to the engine output shaft through a main clutch, and a belt transmission means to branch out power from the first transmission shaft and pass it to a second transmission shaft. The first transmission shaft transmits the drive through the disk type frictional stepless change speed apparatus to axles borne by a transmission case. The entire transmission system inevitably is large since the main clutch is disposed at a separate position from the belt transmission means. Therefore, it has been a pending problem how to make the transmission system and its peripheral elements compact.